1. Technical Field
The present disclosure relates to a self-adaptive surge-proof circuit (SASPC) of inrush-current at start and lightning-surge at operation of a power supply.
2. Description of Related Art
With the rapid development of power supply technologies, switching power supplies have become small and efficient compared to traditional linear power supplies and thus are widely used. Particularly, the switching power supplies have taken place of the linear power supplies to play important roles in fields including but not limited to computers, telecommunications, industrial controls, instruments and apparatuses, and medical equipments.
In practical applications of the power supplies in the fields of telecommunications and industrial controls, the power supplies are often used in terrible environments, which bring forward more strict requirements on the performance of the power supplies. For example, the power supply operation temperature may be from minus 40 degree C. to 50 or even 75 degree C. Moreover, an inrush-current, at start time, and a lightning-surge at operation time may damage components in the circuit or even ruin the power supply. Therefore, a negative temperature coefficient (NTC) resistor is designed in the circuit to prevent the inrush current, and a metal oxide varistor is designed as a lightning-arrestor to prevent the lightning-surge coming from the power grid.
Generally, the inrush-current suppressor includes the NTC resistor, or a silicon controlled rectifier (SCR) connected in parallel with a resistor, or a relay connected in parallel with a power resistor. The thermistor used in the inrush-current suppressor can increase an input impedance of the power supply, thereby limiting the inrush-current in the condition of cold start. However, with the thermistor, the efficiency of the power supply is reduced, which results in a power-on inrush-current in the condition of hot start. With the SCR and the resistor connected in parallel, a high-low temperature may less impact the performance of the power supply. However, as for high-power converter, a driving winding is required, which increases the power dissipation of power supplies. As for the inrush-current suppressor that includes the NTC resistor or power resistor and the relay connected in parallel, although the inrush-current can be limited, the damage caused by the lightening-surge and an overvoltage cannot be avoided as the input impedance is much less than MOV impedance when the relay is in operation. Therefore, there is room for improvement in the art.